The present invention generally relates to automatic transmissions. More particularly, the present invention pertains to a hydraulic pressure control device for an automatic transmission which shifts a gear stage by controlling the hydraulic pressure to be applied to a plurality of friction engaging elements.
In a known type of hydraulic pressure control device for an automatic transmission, control pressure is applied to a plurality of friction engaging elements by way of a corresponding linear solenoid valve depending on the shift signal. In this device, the application of the control pressure to one friction engaging element is carried out through use of a particular linear solenoid valve so that by controlling the energization of each of the linear solenoid valves, it is possible to apply the control pressure to the corresponding friction engaging element.
However, in this known device, the number of linear solenoid valves required for effecting engagement of the friction engaging elements is equal to the number of friction engaging elements. The result is a rather expensive device because linear solenoid valves are relatively expensive. Also, the energization control of each of the linear solenoid valves which is required for shifting becomes relatively complex, thus increasing the overall cost associated with the device.
To address this problem, it has been proposed to apply control pressure to a several of the friction engaging elements by switching one linear solenoid valve. This hydraulic pressure control device is configured to operate such that a control pressure outputted from a sole control valve under the control of a linear solenoid valve is applied to a plurality of friction engaging elements by way of a shift valve which is switched by an ON-OFF solenoid valve. The shift valve is switched depending on the gear stage to be produced in order to cause the shift valve to engage or disengage each of the associated friction engaging elements. According to this device, the ON-OFF solenoid valve, which is relatively inexpensive when compared to a linear solenoid valve, is combined with a linear solenoid valve. As a result, the number of linear solenoid valves in the control device can be reduced relative to the number of friction engaging elements, thus establishing an advantage from the standpoint of cost.
However, in this device, when performing a jumping shift (e.g., a shift from the fifth gear stage to the third gear stage or a shift from the third gear stage to the fifth gear stage) or a multiple shift (i.e., during a shift to one specific gear stage, another shift is made to another gear stage by changing the shift command), it is necessary to switch the shift valve and the friction engaging elements to be applied with the respective control pressure from the control valve at the same time. More specifically, a shift valve switching operation must be performed involving switching the energization condition of the ON-OFF solenoid valves, and at the same time the energization of the linear solenoid valves must be controlled to control the control pressure. In such a case, the control valve which applies the control pressure to the shift valve is switched and a switching operation of the shift valve is performed by switching the energization condition of the ON-OFF solenoid valve. Thus, to produce the desired gear stage, the timing of the switching of the shift valve must be synchronized with the timing of the switching of the control valve which applies the control pressure to the shift valve. However, experience shows that a time lag appears which ranges from initiation of the output of the switching signal to the ON-OFF solenoid valve for switching the ON-OFF solenoid valve to termination of the switching of the shift valve, and another time lag also appears which ranges from initiation of the output of the adjusting pressure from the linear solenoid valve after energizing control thereof to the output of the control pressure from the control valve to the shift valve. It is thus quite difficult to synchronize the shift valve switching with the control valve switching, and this may cause termination of the switching operation of the linear solenoid valve prior to a termination of the switching of the shift valve and/or vice versa. Under such situations, shift related problems or drawbacks may occur such as insufficient application of the control pressure to the required friction engaging element and/or application of the control pressure to an unnecessary friction engaging element.
Thus, a need exists for a hydraulic pressure control device for an automatic transmission that is not as susceptible to the difficulties and a drawbacks mentioned above.
More particularly, a need exists for a hydraulic pressure control device for an automatic transmission that can more reliably establish a desired shift by controlling the application of control pressure to the friction engaging elements by way of a shift valve.
According to one aspect of the invention, a hydraulic pressure control device for an automatic transmission includes a plurality of linear solenoid valves each of which adjusts a hydraulic pressure outputted from an oil pump and outputs an adjusting pressure in response to a current applied thereto, a plurality of control valves each connected to one of the linear solenoid valves and outputting a control pressure in response to the adjusting pressure outputted from the corresponding linear solenoid valve, and a plurality of friction engaging elements each engaged or disengaged depending on the control pressure applied thereto, with the friction engaging elements producing a plurality of gear stages of the automatic transmission depending on combinations of different engaged and disengaged conditions of the friction engaging elements. In addition, a plurality of shift valves are each connected to one of the control valves to switch the friction engaging elements to which the control pressure is applied depending on the hydraulic pressure applied to the shift valves, and a plurality of ON-OFF solenoid valves are each connected to one of the shift valves to control application of the hydraulic pressure to each of the shift valves through energized conditions of the ON-OFF solenoid valves. A control unit controls application of current to each of the linear solenoid valves and the ON-OFF solenoid valves, and controls the adjusting pressure applied to each of the control valves and the control pressure applied to each of the friction engaging elements by controlling the hydraulic pressure applied to each of the shift valves. The control unit establishes a first shift pattern and a second shift pattern which produce gear stages by different combinations of energized or deenergized conditions of at least some of the ON-OFF solenoid valves. The control unit establishes an intermediate shift pattern during a transfer from the first shift pattern to the second shift pattern, such that the intermediate shift pattern makes it impossible to apply the control pressure from a specific control valve to the friction engaging element in case the friction engaging element to which the control pressure is applied from the specific control valve under the first shift pattern differs from the friction engaging element to which the control pressure is applied from the specific control valve under the second shift pattern by switching the shift valve.
In accordance with the present invention, in a shift control in which a shift is made such that switching the shift valve and switching the control valve are made concurrently during transfer from the first shift pattern to the second shift pattern, the application of control pressure from the specific control valve to the friction engaging element in the intermediate shift pattern is prevented. Next, during transfer from the intermediate shift pattern to the second shift pattern, the specific control valve from which application of control pressure in the intermediate shift pattern was prevented, is now able to apply control pressure to another friction engaging element other than the friction engaging element to which it applied control pressure in the first shift pattern. Thus, transfer is made from the first shift pattern to the second shift pattern.
Thus, in situations where a different friction engaging element is applied with control pressure from the specific control valve in the first and second shift patterns, the intermediate shift pattern produces a condition under which the application of the control pressure from the specific control valve to the friction engaging element is prevented (i.e., made impossible). As a result, there is a reduced need or no need for synchronization between the time lag ranging from the outputting of the switching signal to the ON-OFF solenoid valve from the control unit to the termination of the switching of the shift valve and the time lag ranging from the initiation of the energization control of the linear solenoid valve to the outputting of the control pressure from the control valve as a result of the outputting of the adjusting pressure from the linear solenoid valve, which fails to cause termination of the switching operation of the linear solenoid valve prior to a termination of the switching of the shift valve and/or vice versa. Under such situations, little or no shift related problems or drawbacks occur such as insufficient application of the control pressure to the required friction engaging element and/or application of the control pressure to an unnecessary friction engaging element. Thus, the shift control performance is remarkably increased.
The aforementioned specified control valve refers to a designated valve selected from the plural control valves. The specified control valve in the first shift pattern is same as the specified control valve in the second shift pattern.
In addition, the linear solenoid valve is a valve which is capable of outputting the adjusting pressure in a continual mode depending on the amount of current energized or supplied thereto, utilizing the hydraulic pressure or oil pressure outputted from the oil pump directly or indirectly via another valve. The ON-OFF solenoid valve is a valve which is capable of switching the shift valve on-and-off mode depending on its energized and deenergtzed condition.
According to another aspect of the invention, a hydraulic pressure control device for an automatic transmission includes a plurality of linear solenoid valves each of which adjusts a hydraulic pressure outputted from an oil pump and outputs an adjusting pressure in response to a current applied to the linear solenoid valve, a plurality of control valves each connected to a respective one of the linear solenoid valves to output a control pressure in response to the adjusting pressure outputted from the respective linear solenoid valve, and a plurality of friction engaging elements each of which is engaged or disengaged depending on the control pressure applied thereto. The friction engaging elements produce different gear stages of the automatic transmission depending on different combinations of engaged and disengaged conditions of the friction engaging elements. A plurality of shift valves are each connected to one of the control valves to switch the friction engaging elements to which the control pressure is applied depending on the hydraulic pressure applied to the shift valves, and a plurality of ON-OFF solenoid valves are each connected to one of the shift valves to control application of the hydraulic pressure to each of the shift valves through energized and deenergized conditions of the ON-OFF solenoid valves. A control unit controls application of current to each of the linear solenoid valves and the ON-OFF solenoid valves, and controls the adjusting pressure applied to each of the control valves and the control pressure applied to each of the friction engaging elements by controlling the hydraulic pressure applied to each of the shift valves. The control unit establishes a plurality of shift patterns producing gear stages by different combinations of energized or deenergized conditions of at least some of the ON-OFF solenoid valves. The plurality of shift patterns include one shift pattern producing at least two gear stages and a different shift pattern producing at least two gear stages, with one of the gear stages in the one shift pattern being the same as one of the gear stages in the different shift pattern. One of the control valves applies control pressure to one of the friction engaging elements during the one shift pattern and applies control pressure to a different friction engaging element during the another shift pattern. The control unit is adapted to establish during transfer from the one shift pattern to the another shift pattern an intermediate shift pattern during which control pressure from the one control valve to the one friction engaging element is prevented.
In accordance with another aspect of the invention, a method of shifting an automatic transmission involves supplying control pressure from a plurality of control valves to a plurality of friction engaging elements to effect engagement and disengagement of different combinations of the friction engaging elements and produce a plurality of different gear stages, establishing one shift pattern that includes at least one gear stage, transferring to a different shift pattern that includes a gear stage different from the one gear stage, and prohibiting application of control pressure from one of the control valves to one of the friction engaging elements during transfer from the one shift pattern to the different shift pattern when the one control valve applies control pressure to the one friction-engaging element under the one shift pattern and applies control pressure to another friction engaging element different from the one friction engaging element under the different shift pattern.